When is a good time to see the fall colors and the rutting season
The fall colors are generally best the 3rd and 4th weeks of September. The elk rut is mid-September through mid-October.
RMNP rangers posted this FAQ answer on Facebook and Twitter last year about fall color.
"Fall comes early to the high country. Up high the tundra turns to shades of autumn russets, reds, and oranges as August progresses.
Years vary, but generally in the last week of August the first gold aspen leaves start showing up, high on hillsides.
In early September, leaves start turning gold in the Grand Lake area.
Weather (rain, snow, wind) can affect when the trees turn, and can even cause the leaves to fall early."
Because the combination of fall color and elk rut in RMNP is so appealing to so many people, I strongly encourage you to visit RMNP during the week and not on a Friday, Saturday or Sunday. The crowds are overwhelming. If history is any indication, the weekends of September 22 (free day in the park) and 23 and September 29/30 (Elk Fest in Estes Park) will be among the highest visitation weekends of the entire year in RMNP.
If you are talking about the weekend of September 22/23, all of RMNP will be busy including the west side, but the west side between Grand Lake and Far View Curve will not be nearly as crowded as the more popular east side. By the weekend of September 29/30, the west side of the park and Grand Lake are not usually that busy. By then, the leaves on the west side of RMNP and in the Grand Lake area are often past peak. In later September, Trail Ridge Road can be temporarily closed as a through road due to snow at higher elevations. That is another reason visitation to the west side of RMNP and Grand Lake tapers off toward the end of September.
While the elk rut happens on both sides of RMNP. There are more elk herds and harems and more areas to observe the elk rut on the east side and in Estes Park. On the west side of RMNP, elk congregate in the Harbison and Holzwarth Meadows. Observe the elk protection closures in these areas.
You can add the Guanella Pass Scenic Byway (another great fall color drive) to the above route.
Thank you for all the important info we will be traveling down hwy 125 outside of Wyoming and going to the park in that direction we plan to arrive Sept 22nd still hoping to see some color have been to the park before one if not the best nat parks we have visited color or no color still will enjoy it's beauty